This invention relates to light emitting elements, and more particularly, to improving the performance characteristics of light emitting elements.
Light emitting elements such as light emitting diodes (LEDs), laser diodes, and vertical cavity surface emitting lasers (VCSELS) are used today in a wide variety of electronic applications. Common examples of products that employ light emitting elements include DVD players and high speed optical communications systems. Frequently, the role of light emitting elements involves the generation of light pulses for data acquisition or transmission. To function in this capacity, driver circuitry is typically utilized to supply the appropriate electrical differential across the light emitting element to generate digital optical signals.
Currently, many light emitting elements are fabricated with varying impedance values. A VCSEL, for example, typically has an impedance value that varies between about 17-50 Ohms. This variation poses problems for driver circuitry because of the likely impedance mismatch that results between the output of the driver circuitry and the input of the VCSEL. Foremost among these problems are the signal reflections that occur along the transmission line between the driver circuit and the VCSEL that reduce signal quality and limit response time.
Presently, this problem is dealt with by manipulating the operating characteristics of the driver circuitry. One popular solution, for example, includes the addition of external termination components that absorb reflected energy. This solution is not optimal because it requires system manufacturers to determine the impedance of each light emitting element individually and couple the appropriate compensation components to the driver circuitry. Other popular solutions include the use of precision driver modules that can accommodate an impedance mismatch without losing significant performance. Such systems, however, inevitably sacrifice certain amounts of bandwidth and frequency response.
Thus, in view of the foregoing, it would be desirable to provide circuits and methods that reduce or minimize the impedance variation associated with light emitting elements.
It would also be desirable to provide circuits and methods that enable adjustment of the transfer function associated with light emitting elements to improve or optimize certain performance attributes.